1. Technical Field:
The present invention relates to safety pressure relief devices and more particularly to rupture disks. Even more particularly, the present invention relates to reverse-buckling tupe rupture disks of the type using a reverse-buckling rupture disk in combination with a knife located downstream of the concave side of the rupture disk.
2. General Background:
Various rupture disks have been patented of the reverse-buckling type, which in combination with the disk use a cutting blade for severing the disk when the disk reverses and buckles in the presence of a design relief pressure. Notice, for example, recently issued U.S. Pat. No. 4,269,214 entitled "Safety Pressure Relief Valve" issued to Calvin C. Forsythe, John L. Strelow and Miner E. Clift, the latter being a co-inventor of the present application. In that application, there is discussed various prior reverse-buckling type rupture disks which have as part of the apparatus a cutting blade for severing a portion of the disk upon reversal. In the patent, there is provided a safety pressure relief device including a rupture disk having a concave-convex portion and a radially outer flange portion joined by a curved transition connection. A knife is located adjacent the concave side of the rupture disk, with the knife including a radially outer flange portion which supports the curved transition connection. A substantially circular inner opening is disposed within the knife. The knife includes first and second spaced cutters projecting radially inward into the opening and inclined toward the concave portion of the rupture disk. The knife further includes first and second arcuate non-cutting portions each partially defining an inner opening. The first cutting blade is located between the first and second non-cutting portions so that upon reversal of the rupture disk, the first and second cutting means will puncture the rupture disk without severing a portion of the disk therefrom.
Another safety pressure relief apparatus of the reverse-buckling type is U.S. Pat. No. 4,211,334 issued to John E. Witten, Loren E. Wood and Edward Short. That device provides a safety pressure relief apparatus having a reverse-buckling rupture disk which provides a concave-convex portion connected to an annular flat flange portion by a curved transition connection and a support member having an annular flat flange portion for engaging the annular flat flange portion of the rupture disk and for supporting the transition connection thereof. The support member includes a cutting edge positioned interiorly of the transition connection and forming an opening in the support member so that when the concave-convex portion of the rupture disk reverses itself, the cutting edge severs the disk whereby a portion thereof passes through the opening in the support member. A bar for catching the severed portion of the disk after it passes through the opening in the support member is attached to the support member.
Another reverse-buckling type rupture disk is seen in U.S. Pat. No. 3,908,684 issued to Edward Short. That device provides a rupture disk assembly of small integral construction comprising a substantially cylindrical housing having a reverse-buckling rupture disk supported therein. An annular top supporting member is positioned within the housing adjacent to the rupture disk, which includes an annular lip portion extending outwardly around the periphery thereof. The upper end portion of the housing is folded over the outwardly extending lip portion of the supporting member so that the lip portion is deformed downwardly thereby rigidly clamping the supporting member and rupture disk within the housing.
A low pressure rupture device is the subject of U.S. Pat. No. 4,119,236 issued to Kenneth R. Shaw and Franklin Hansen. That patent discloses a safe pressure relief assembly of the reverse acting rupture disk type which guards against very low pressure differentials and includes a thin, bulged sealing disk, a cutting member positioned in spaced relation to the sealing disk and extending a substantial transverse distance thereacross and a sealing disk support member having a stay arrangement projecting into support engagement with the concave side of the sealing disk, the stay arrangement having a resistance to collapse sufficient to retain the sealing disk out of contact with the cutting member only up to a predetermined differential pressure.
A precise, reverse acting, frangible disk pressure device is the subject of U.S. Pat. No. 3,685,686 issued to John H. Raidl. That device uses a frangible member sub-assembly having a pre-bulged frangible disk with its annular flange secured between first and second seating rings. The frangible disk sub-assembly and a co-acting knife blade sub-assembly are mounted in annular grooves on the mating faces of flanges. A particular feature is the supporting of the downstream disk seating ring against an annular seat on the knife blade sub-assembly so that the device will not seal against pressure in the event the knife blade sub-assembly is inadvertently omitted.
U.S. Pat. No. 3,693,691 entitled "Pressure Relief Device" was issued Sept. 26, 1972 to Stanley Summers. That device provides a device particularly suited for use with aircraft wheels or similar wheel bearing tires which are inflated with a gas from a source that is at a pressure that exceeds the safety limits of the wheel.
Many of the above devices require complex manufacturing as they include a number of complex interconnecting parts, ridges, shoulders, and the like. These devices are highly complex, expensive to manufacture and to machine and are generally costly. Further, many of these devices provide cutting blades which can, in fact, support the disk during reverse-buckling rather than cut the disk, causing malfunction. For exaple, many of the knife blades used in such reverse-buckling disks are a plurality of knife blades which, upon reversal, cut the disk into radial sections such as quarters. Some of these knife blades require finely honed edges in order to function properly. Corrosion, for example, can severely limit proper operation of such a rupture disk. Another problem with rupture disks is the problem of a full opening of the disk upon rupture. This problem can be particularly acute at low pressures. Another problem of some reverse buckling knife type rupture disks is the problem of reusing portions of the disk such as the knife and/or disk. Many existing rupture disk devices are permanent assemblies which are "throw-away" after one use.